1. Technical Field
The disclosure relates to composite micropowder including fluorine-containing polymer, and in particular to the method and application thereof.
2. Description of the Related Art
Fluorine-containing polymers, especially polytetrofluoroethylene (PTFE), are the most chemically inert of all polymers. The fluorine-containing polymers have specific climate resistance, electrical insulation, low friction coefficients, and chemical resistance, thereby being widely applied in airlines, vehicles, petroleum, chemical engineering, and the like. Fluorine-containing polymer micropowders (especially PTFE micropowder) have a small diameter and enough softness to be evenly dispersed in other base materials to enhance those base materials' properties, e.g. lubricity, abrasion resistance, scratch resistance, releasing property, pollution resistance, flame retardancy, and hydrophobicity, and the like. As such, the major application of the fluorine-containing polymer micropowders is additive of other materials (e.g. paint). The PTFE micropowder has a smaller diameter, e.g. 4 μm to 10 μm, such that a paint with PTFE micropowder added may form a non-stick film with a smoother surface. In the paint system of polyether sulfone and polyphenylene sulfide, the PTFE micropowder is usually added into the paint for spray coating on a substrate. The paint is baked at a high temperature of 380° C. to 400° C. to have enough releasing ability, thereby being widely applied as the coating film of an automatic cooker. In addition, polychlorotrifluorothylene (PCTFE), tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene difluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), or ethylene-trifluorochloroethylene copolymer (ECTFE) has a diameter of 20 μm to 80 μm and excellent properties, thereby being usually applied as a powder coating.
Commercially available middle-coarse powder of fluorine-containing polymer such as PTFE has a diameter of about 70 μm to 260 μm. The commercially available fine powder of PTFE has a diameter of about 20 μm to 50 μm. The commercially available product directly added into the paint is easily aggregated and dispersed with difficulty, such that the paint properties are easily degraded or particles are formed on the coating film surface. Accordingly, the commercially powder should be further refined to reduce its diameter. Because PTFE has a low crystallinity and a low softening point, it is difficult to directly crush to ultra-fine the PTFE by a physical method. Next, the directly crushed PTFE powder has problems such as non-uniform diameter, poor flowability, large diameter, and the like.
The commercially available PTFE micropowder has a diameter of about 0.5 μm to 15 μm. The paint with added PTFE micropowder may form a coating film with an excellent smooth surface. The majority of methods of preparing PTFE micropowders can be a telomerization method, pyrolysis method, or radiation cracking method.
The telomerization method can be referenced in U.S. Pat. No. 5,641,571 and U.S. Pat. No. 3,956,000. The fluorine-containing polymer is first dispersion polymerized to form a dispersion liquid, and then aggregated and precipitated from the dispersion liquid to form micropowder. For example, the PTFE micropowder can be Dyneon™ PTFE TF-9201 and TF-9207 (diameter of 4 μm to 6 μm) commercially available from 3M Corporation. The telomerization method has multiple steps, and the micropowder product thereof has a low molecular weight (e.g. weight average molecular weight of about 200,000).
The pyrolysis method can be referenced in U.S. Pat. No. 3,813,449 and U.S. Pat. No. 4,076,760. The PTFE raw material is charged at a high temperature of 450 to 600 under a high pressure of 5×101.325 kPa to 10×101.325 kPa. The PTFE is pyrolyzed with shearing force and friction force to obtain a low molecular weight PTFE, which is then ground to obtain a PTFE micropowder. For example, the PTFE micropowder can be Dyneon™ PTFE TF-9205 (diameter of 8 μm) commercially available from 3M Corporation. However, the pyrolysis method consumes a lot of energy and produces a decomposition product with high toxicity.
The radiation cracking method can be referenced in U.S. Pat. No. 3,766,031, GB Pat. No. 2119385, and EP Pat. No. 0253400. The carbon chain of the PTFE is degraded by high-energy radiation such as γ-ray or E-beam to prepare a low molecular weight PTFE, which is then ground to obtain a PTFE micropowder with a diameter of 5 μm to 10 μm. For example, the PTFE micropowder can be Dyneon™ PTFE J14 (diameter of 6 μm) commercially available from 3M Corporation. However, the radiation cracking method requires specialized radiation equipment and incurs a high cost. In addition, the PTFE degraded by the radiation has a low molecular weight, thereby reducing its non-stick properties.
A ceramic paint is an aqueous inorganic paint with a major composition of nano inorganic compound dispersed in water. The ceramic paint is coated and then solidified by low-temperature heating, thereby obtaining a coating film similar to ceramic. The ceramic coating film has several advantages such as high thermal resistance, high hardness, climate resistance, and being environmentally friendly. The ceramic coating film is quickly applied in kitchenware due to its safety, but its non-stick properties cannot be sustained for along period. The non-stick properties of the ceramic paint come from silicon oil such as polydimethylsiloxane or hydroxypolydimethylsiloxane. However, the silicon oil in the ceramic paint gradually evaporates through cooking, such that the ceramic paint will lose its non-stick properties. Because a detergent for washing woks or pans is usually alkaline, the silicon oil on the coating surface and in the coating is easily washed out by the detersive at high temperatures in alkaline conditions. If a fluorine-containing polymer such as PTFE or PFA is added into the ceramic paint, the non-stick properties of the ceramic paint will be sustained for a long period. Moreover, defects such as being too soft, having insufficient abrasion resistance, and insufficient hot hardness of the fluorine-containing polymer (e.g. PTFE) film can be overcome, too. Compared to commercially available PTFE micropowder, the composite micropowder of PTFE and polysiloxane in the disclosure has better capabilities and non-stick properties for the ceramic paint.